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The invention of photosynthesis is often cited as one of the keystone events in the evolution of life on Earth. Roughly 2.5 billion years ago, oxygenic photosynthesis—the type of photosynthesis most of us are familiar with—provided the first major pulse of oxygen into a microbial world that was essentially anaerobic and ill-equipped to cope with what was effectively poisonous gas. Nonetheless, life found a way to adapt to this increasingly oxygenated atmosphere, and the ensuing transformation of the biosphere left indelible marks in the core biochemical reactions that complex life is now dependent on. Indeed, the rise of oxygen not only correlates with but has been argued to be ultimately responsible for the evolution of complex, intelligent life on our planet—and may be a key biomarker for finding habitable worlds elsewhere in our galaxy.
Our lab uses a variety of methods to trace the biochemical transformations that accompanied the rise of oxygen in Earth’s early atmosphere. Among these transformations are familiar examples, such as the ramped-up production of ATP through aerobic respiration (which biology students will tell you is up to 20 times as efficient as ATP production through fermentation). However, our research has uncovered hundreds of different biochemical reactions that have been modified as a result of oxygen’s availability. In effect, the circuitry of metabolism has been extensively rewired following the availability of O2, and the ancestors of modern-day aerobes developed a repository of new compounds that have become key to the function and survival of complex lifeforms.
In this presentation, I detail our work in advancing the understanding of how biochemistry changed as a result of the availability of oxygen. Our methods integrate classical tools from evolutionary biology with genome-enabled models of microbial metabolism, to reconstruct how genomes have evolved through Earth’s history. Linking these reconstructions with our colleagues’ geological and geochemical insights on Earth’s earliest biospheres is providing important insights into how biology and environment have co-evolved in the past, and how the two will continue to shape each other as modern Earth continues to undergo global-scale changes.